16 April 2004 SAGENAP

A reactor experiment to measure 13

• APS neutrino study

• Importance of 13

• Unique role of reactor experiments• Conclusion

E. Blucher, Chicago

Reactor working group: explore possibilities for neutrino physics with nuclear reactors

Erin Abouzaid, Kelby Anderson, Gabriela Barenboim, Andrew Bazarko, Eugene Beier, Ed Blucher, Tim Bolton, Janet Conrad, Joe Formaggio, Stuart Freedman, Dave Finley, Peter Fisher, Moshe Gai, Maury Goodman, Andre de Gouvea, Nick Hadley, Dick Hahn, Karsten Heeger, Boris Kayser, Josh Klein, John Learned, Manfred Lindner, Jon Link,

Bob McKeown, Irina Mocioiu, Rabi Mohapatra, Donna Naples, Jen-chieh Peng, Serguey Petcov, Jim Pilcher, Petros Rapidis, David Reyna, Byron Roe, Mike Shaevitz, Robert Shrock, Noel Stanton, Ray Stefanski (+ Thierry Lasserre, Hervé de Kerret)

APS Study: Identify key questions of neutrino physics and evaluatemost promising experimental approaches to answering them. written report in summer 2004

Broad participation from community:

Working groups formed to explore particular experimental approaches:Solar/atmospheric, accelerators, reactors, neutrino factories, 0 decay, cosmology/astrophysics

Neutrino physics at nuclear reactors

E.g., early studies indicate that a measurement of sin2W with precision comparable to NuTeV could be performed using e – e scattering.

Use the antineutrino-electron elastic scattering

e

e

ZW

ddT

G2m 2 {(CV+CA)2 +(CV-CA)2 (1- )2 + (CA

2-CV2) mT

E T E2=

CV = ½ + 2 sin2 W

CA = ½

T = electron KE energyE = neutrino energym= mass of electronThis assumes =0

The total rate for this process is sensitive to sin2 W

(ES)

}

e

e

(Conrad, Link, Shaevitz, hep-ex/0403048)

+ several additional possibilities: sin2W, solar m2, neutrino magnetic moment, SN physics, CPT tests

International Workshops:Alabama, June 2003Munich, Germany October 2003Niigata, Japan, March 2004Paris, France, June 2004

APS reactor study builds on work presented in series of international workshops, andwritten up in whitepaper.

APS reactor group meetings:Argonne, December 2003Chicago, February 2004May 2004

Neutrino Oscillations

• During last few years, oscillations among different flavors of neutrinos have been established; physics beyond the S.M.

• Mass eigenstates and flavor eigenstates are not the same (similar to quarks):

1 2 3 1

1 2 3 2

1 2 3 3

e e e eU U U

U U U

U U U

mass eigenstatesflavor eigenstates

• Raises many interesting questions including possibility of CP violation in neutrino oscillations.

• CP violation in neutrino sector could be responsible for the matter-antimatter asymmetry.

MNSP matrix

1 2

1 2 3

1 2 3

12 12 13 13

12 12 23 23

13

3

13 23

cos sin 0 cos 0 sin 1 0 0

sin cos 0 0 1 0 0 cos sin

0 0 1 sin 0 cos

?

0 sin co

CP

CP

ee e

i

i

U U Big Big

U U U U Big Big Big

U U U

U

Big Big Big

e

mall

e

S

23s

12 ~ 30° 23 ~ 45°sin2 213 < 0.2 at 90% CL

What is e component of 3 mass eigenstate?

What do we know?

normal inverted

•What is value of 13?

•What is mass hierarchy?

•Do neutrino oscillations violate CP symmetry?

P( e ) P( e ) 16s12c12s13c132 s23c23 sin sin

m122

4EL

sin

m132

4EL

sin

m232

4EL

Value of 3 central to these questions; it sets the scale for experiments needed to resolve mass hierarchy and search for CP violation.

Key questions

•Why are quark and neutrino mixing matrices so different?

1

~ vs.

?

~ 1

1MNSP CKM

Big Big Small Small

U Big Big Big V

Sm

Small Small

Big Big Big Small Small

all

Methods to measure sin2213

• Accelerators: Appearance (e)

• Reactors: Disappearance (ee) 2

2 2 1313( ) 1 sin 2 sin very small terms

4e e

m LP

E

22 2 2 213

23 13 13( ) sin sin 2 sin not small terms ( , ( ))4e CP

m LP sign m

E

Use fairly pure, accelerator produced beam with a detector a long distancefrom the source and look for the appearance of e events

T2K: <E> = 0.7 GeV, L = 295 km NOA: <E> = 2.3 GeV, L = 810 km

Use reactors as a source of e (<E>~3.5 MeV) with a detector 1-2 kms awayand look for non-1/r2 behavior of the e rate

Reactor experiments provide the only clean measurement of sin22: no matter effects, no CP violation, almost no correlation with other parameters.

2atmm 2

solarm2 2

2 2 2 213 1213 12( ) 1 sin 2 sin sin 2 sin

4 4e e

m L m LP

E E

Reactor Measurements of ( )e eP

13: Search for small oscillations at

1-2 km distance (corresponding to 2 ).atmm

Distance to reactor (m)

Pee

2 3 213

213

2.5 10

sin 2 0.04

3.5

m eV

E MeV

Past measurements:

Chooz: Current Best Experiment

L=1.05 km

P=8.4 GWth

D=300mwe

m = 5 tons, Gd-loaded liquid scintillator

sin22< 0.2 for m2=2103 eV2

CHOOZ Systematic errors

Reactor flux

Detect. Acceptance

2%

1.5%

Total 2.7%

,e p e n Neutrino detection by 8 of s; ~ 30 secn Gd MeV

How can Chooz measurement be improved? Add near detector: eliminate dependence on reactor flux calculation; need to understand relative acceptance of two detectors rather than absolute acceptance of a single detector + optimize baseline, larger detectors, reduce backgrounds

~200 m ~1500 m

Issues affecting precision of experiment:• Relative uncertainty on acceptance• Relative uncertainty on energy scale and linearity• Background (depth)• Detector size• Baseline• Reactor power

Study has focused on three scales of experiments:

• Small sin2213 ~ 0.03-0.04 (e.g., Double-Chooz)

• Medium sin2213 ~ 0.01 (e.g., Braidwood, Diablo Canyon, Daya Bay)

• Large sin2213 < 0.01

For each scenario, understand cost, timescale, and physics impact.

Ref. hep-ph/0403068

Strong consensus in working group that experiment withsensitivity of sin2213~0.01 should be our goal.

• If sin22 < 0.01, it will be difficult for long-baseline “superbeam” experiments to investigate mass hierarchy and CP violation.

Reactor experiment with sensitivity of 0.01 will indicate scale of future experiments needed to make progress.

• If sin22 > 0.01, a precise measurement will be needed to combine with accelerator experiments.

+/- 0.028

cp— normal— inverted

m2=2.510-3 eV2

Both reactor and accelerator experiments have sensitivity tosin22, but accelerator measurements have ambiguities

Example: T2K. P(e)=0.0045 sin2213=0.028

(5 yr

3 Limits

Reactor with sensitivity of

sin22~0.01 at 90% c.l. (3~0.018)

Reactor and accelerator sensitivities to sin22

NOA

Example: FNAL Off-Axis (NOA)

sin22<0.04

2 limits for resolutionof mass hierarchy for3 years of and 3 yearsof running

Value of sets scale of experiment needed to resolve mass hierarchy and study CP violation.

sin22<0.01 Possible reactor limits

NOA(5 yr )

Reactor(+/- 0.01)

CP

normal

inverted

m2=2.5x10-3 eV2

Complementarity of reactor and accelerator experiments

CP

P(

e

)

Searching for CP violation

sin2213=0.1

T2K

P(

e

)

CP

sin22=0.01from reactor

T2K - 5 years

Neutrino, normal hierarchy

Neutrino, inverted hierarchy

Example: Reactor + T2K running

sin2213=0.1

CP Measurement(with / without Reactor)

JHF+NuMI

JHF+NuMI+Reactor

JHF

= 270

JHF+Reactor

sin2213=0.06

Conclusions

• Extremely exciting time for neutrino physics!

• Value of sin22 sets the scale for experiments needed to study mass hierarchy and CP violation

• Reactor experiment has potential to be fastest, cheapest, and cleanest way to establish value of

• Reactor experiment with sensitivity of sin22~1% will give information needed to understand future roadmap of neutrino program

• Reactor and accelerator experiments are complementary: reactor information improves sensitivity of accelerator experiments to CP violation and mass hierarchy